Apparatus and method to reduce noise emanating from a ventilation fan

ABSTRACT

An apparatus and method for suppressing ventilation fan noise by covering fan blades and optionally duct with sound absorbing liner made out of soft flexible durable material such as felt. Another apparatus and method is encasing the fan unit in a sleeve made out of sound blocking, antivibration materials, such as mass loaded vinyl, rubber for housing portion, and sound absorbing materials, such as acoustic blankets for sleeve extension or combination of both. A preferred method includes covering the fan blades permanently or removably with felt liner in a way that the whole blade is covered and extra fringe material is trailing off the edge of the blades. The sound dampening casing includes duct case made out of mass loaded vinyl and rubber and the extension sleeve made out of sound absorbing material such as acoustic blanket. 
     The sound dampening sleeve is flexible and can be folded or rolled away to save space for storage or transportation

BACKGROUND OF THE INVENTION

This invention relates generally to the field of fans, ventilation duct fans and more particularly to reduction of noise produced by fan blades and air turbulation. Ventilation fans are widely used to blow and circulate air in enclosures, such as buildings, rooms, sound booths, green-houses etc. Ventilation fans are a necessity and they come in many different models and sizes from variety of manufacturers and for variety of applications. At the same time noise that they create is undesiarable in residential homes, offices, or factories. Noise pollution can be harmful to health, decreses productivity, and is extremely unwanted and even critical in specialized environments such as vocal booths, recording studios, hospitals, and many other places and applications where silence is a must. New fans are being developed claiming to be less noisy, but they require a purchase of that new fan, while the existing fans are still functional. Therefore there is a need to develop a method of reducing the noise in existing fans as a post production application, and also use that method to manufacture a silent fan of a new design.

The noise from a working fan, for example a duct ventilation fan, comes from two major sources: the motor/engine and blades action creating air turbulence at the edge of the blades and rushing air in the fan housing case.

Previous art was dealing mostly with capturing noise carried with the air blown by the fan.

The method described in this invention prevents the noise from being generated at the source, or by the blades themselves. It cancels the sounds created by the air turbulence caused by the rotating blades of the fan.

As the rotating blades cut through the air pushing it forward, they create an air turbulence at the blade's edge, emitting a whistling, swooshing noise. The blades themselves are vibrating, creating additional noise as a soundboard, or rattling noise if they are unbalanced. The faster the rotation, the louder the noise. This is especially true for a low cost duct ventilation fans, where the blades are made out of cheap thin sheet metal and the blades and the duct itself are not smooth and aerodynamic. Also if the housing case of the duct fan is made out of the same sheet metal with sharp edges and corners it may cause small air turbulences to form, and add to creation of the whistling noises as the air rushing through the ducts.

Numerous attempts that have been made to reduce the noise from ventillation fans mostly addressed the inflow and outflow of the air.

The disadvantages of the prior technology are that they do not address the issue at the source of the noise to prevent the creation of the noise in the first place, but rather trying to treat the noise after it has aleady been created. Or they require a specially manufactured blades that cannot be made by a non-professional, or cannot be used as an add-on postproduction product to an existing fan to fix the problem. Also there is no suggested method that would allow to treat fan blades in post production by general public or a business that needs an extra quiet fan.

An additional sound dampening sleeve described in this application is designed to treat the noise that is being carried with the air blowing from the fan.

The novelty of this apparatus and method is that they provide a solution to make the existing fans quieter, produce new fan designs with built in quiet fan blade features and the soundabsorbing sleeve that is flexible and can be easily transported, minimizing the volume of the total assembly.

BRIEF SUMMARY OF THE INVENTION

The main object of the invention is to provide means to reduce the noise of a ventilaltion fan.

Another object is to create a method that can be applied to quiet an existing fan post production.

Another object of the invention is to prevent the airborn noise to form at the blade level due to air turbulence.

Yet another object is to prevent the noise created by vibrating of the fan blades. Another object of the invention is to provide a method to easily smooth the sharp hard edges that cause the noise as the air flows through;

Another object is to dampen the transmission of noise created by working duct fan.

The novelty of this invention is the use of material and design features that can be applied in post production to allow to minimize air turbulence, smoothen sharp hard surfaces, add absorbtion quality, light weight, low cost, ease of use and application. The method is applicable to a variety of fan designs and models.

The advantages of this invention over the prior art are high efficiency, low cost of implementation, potential to apply in postproduction to existing fans, simplicity and practicality.

Other objects and advantages of the present invention and method will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A, is a perspective view of a noise cancelling liner for propeller (circular) fan blade application.

FIG. 1B, is a perspective view of a noise cancelling liner for straight (centrifugal) fan blade application.

FIG. 2A, is a perspective view of a propeller fan blades.

FIG. 2B, is a perspective view of a centrifugal fan blade.

FIG. 3A, is a view from the back of the propeller fan blades with the noise cancelling liner attached,

FIG. 3B, is a view from the front side of the propeller fan blades with the noise cancelling liner attached.

FIG. 4, is assembled duct fan inside a housing with the noise cancelling liner attached.

FIG. 5, is an overview of the assembled duct fan with housing, enclosed in the sound absorbing sleeve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Detailed descriptions of the preferred embodiment are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or manner.

Referring now to FIGS. 1-4 there is shown an apparatus for reducing fan noise at the blades level and method of applying the same.

Referring now to FIG. 1A there is shown an overview of the noise cancelling liner 10, for a propeller (circular) type fan, cut in a way that it is larger (wider) than the blades themselves yet only marginaly exceeds diameter of the blades.

Referring now to FIG. 1B there is shown an example of liner 10 cut in rectangular shape for a centrifugal type of fan blade. The cerrated edges 13 are on the trailing part of the liner.

FIG. 2A presents and example of a propeller (circular) type fan blade 20, and FIG. 2B shows an example of centrifugal type fan 30 with straight rectangular blades.

Referring now to FIG. 3A there is shown a view from the back on a propeller blade 20 with sound absorbing layer 10 attached. This figure shows the trailing edge 16 of the liner 10 extending beyond the back edge of the blade 20. The diameter of the Liner 10 is just large enough to cover the very tip 11 of the outer edge of the blade 20. The front edge of each “blade” liner can be applied marginally over the edge of the blade or it can be bent around the edge to the other side to “round up” the front edge of the blade. Trailing edge 16 of each section should be extended over the back edge of the blade to prevent the air turbulence at the back edge of the blade and to create a smooth path of the air flow from one blade to the other. It may be serrated in a comb-like fashion for more efficiency.

Referring now to FIG. 3B is a view from the front of the same propeller fan blade with noise cancelling layer attached. This figure shows that the liner 10 covers whole surface of the fan blades. Center screw 21 is part of the fan blade, serving to attach the blade to the fan motor axle on which the blades rotate.

Referring now to FIG. 4 there is shown assembled duct fan 50 with noise cancelling liner 10 attached to the fan blades, in a housing 52. (Attached power cord 70 serves to power the fan.) An additional liner may be attached to the inside of the housing 52. The noise cancelling liner of the housing would smooth the sharp edges and provide a smooth flow of the air through the duct. The liners also smooth all hard sharp edges and binds the metal parts to dampen the vibration and resonating effect.

It is conceivable that the liner may be made of various suitable sound absorbing materials fibrous or porous in nature, such as felt or foam, or nonresonant such as rubber. Further, the liner may be attached permanently by means of glue, or releasably. Alternatively the liner can be designed and manufactured in a way that it may be pulled over as a “sock” on each undividual blade. Or the blades and/or housing may be specially manufactured to incorporate the noise cancelling liner or turbulence cancelling design, such as hair like surface or soft serrated edge. It is also conceivable that the shape of the liner can be other than circle, as described in the preferred embodyment or the blades may be covered only partially.

Referring now to FIG. 5 there is shown a complete assembly of a duct fan 50 enclosed into a noise dampening sleeve 80, comprising vibration cancelling jacket 81, noise absorbing sleeve 82 and optional flexible duct 83 to direct airflow. Filter 87 serves as a safety device to prevent foreign object from getting into the blades of the fan and also filter the incoming air.

While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

To further clarify the practical use of the invention it should be noted that the noise cancelling liner can be manufactured and distributed separately from a fan and used to attach to the existing fan blades to reduce the noise emanating from it. For example in greenhouse fans, heat exhaust fans in a house, booster duct fans in a house, in HVAC systems and so on. The home ventilation fans or blow fans can be designed using the described method to manufacture the fan blades with the soft trailing edge and soft front “cutting” edges and tip of the blade to reduce the overall fan noise. 

What is claimed is:
 1. An apparatus for suppressing fan noise, the apparatus comprising: a fan blade sound-absorbing liner comprising soft, flexible durable material, attachable to blades of a fan; and a housing sound-absorbing liner comprising flexible durable material and arrangeable to line an inside surface of a fan housing and optionally an air duct.
 2. An apparatus for suppressing ventilation fan noise transmitting with air blowing from a fan, the fan comprising at least one fan blade, the apparatus comprising: a sound-blocking and vibration-cancelling fan housing comprising non-resonant, elastic, flexible material, and a sound-absorbing sleeve comprising flexible durable material and configured for attachment to the fan housing.
 3. A method for treating a fan to reduce emanating noise, the method comprising: attaching a non-resonant sound absorbing liner to blades of the fan, and attaching the liner to an inside housing of the fan.
 4. A fan having fan blades operable to produce an air flow, wherein the fan blades are designed to have a soft sound-absorbing non-resonant surface and/or liner.
 5. The apparatus according to claim 1, wherein the sound absorbing liner has an adhesive surface.
 6. The apparatus according to claim 1, wherein the sound absorbing liner has a surface with a releasable attachment.
 7. The apparatus according to claim 1, wherein the sound absorbing liner attached to the fan blade has a trailing edge that can be straight, serrated or shaped otherwise.
 8. The apparatus according to claim 2, wherein the sound absorbing sleeve is flexible and/or foldable and/or rollable.
 9. The apparatus according to claim 2, wherein the sound absorbing sleeve comprises a flexible attachment configured to direct the air flow.
 10. The apparatus of claim 2, wherein the sleeve comprises a layered wall having a sound absorbing liner as an inner layer and an dense air tight shell as an outer layer.
 11. The method according to claim 3, wherein the attaching is by permanent adhesion to the blades and/or the housing.
 12. The method according to claim 3, wherein the attaching is releasable such as utilizing a hook and loop fastener.
 13. The fan according to claim 4, wherein the fan blade further comprises a plurality of filaments designed, structured and arranged to break air flow and/or reduce turbulence of the air flow.
 14. The fan blade according to claim 4, where it further comprises at least one soft edge, that can be in a serrated comb-like shape.
 15. The apparatus according to claim 1, wherein soft, flexible durable material comprises felt.
 16. The fan blade according to claim 1, where it further comprises at least one soft serrated comb-like edge.
 17. The fan according to claim 1, wherein the serrated comb-like edges are arranged with a trailing edge of the fan blade.
 18. The apparatus according to claim 2, wherein the soft, flexible durable material comprises rubber or mass-loaded vinyl.
 19. The apparatus according to claim 2, wherein the sleeve comprises an acoustic blanket
 20. The method according to claim 3, wherein the fan is a duct fan. 